Optical scanner devices are well-known in the art and produce machine-readable image data signals that are representative of a scanned object, such as a photograph or a page of printed text. In a typical scanner application, the image data signals produced by an optical scanner may be used by a personal computer to reproduce an image of the scanned object on a suitable display device, such as a CRT or a printer. Some examples of optical scanner devices are fax machines, digital copiers, and computer scanners (flatbed and portable).
Optical scanners are well-known in the art and various components thereof are disclosed in U.S. Pat. No. 5,552,597 of McConica for "Hand-Held Scanner having Adjustable Light Path", U.S. Pat. No. 5,586,212 of McConica, et al., for "Optical Wave Guide for Hand-Held Scanner," U.S. Pat. No. 5,381,020 of Kochis, et al., for "Hand-Held Optical Scanner with Onboard Battery Recharging Assembly," and U.S. Pat. No. 5,306,908 of McConica, et al., for "Manually Operated Hand-Held Optical Scanner with Tactile Speed Control Assembly," all of which are hereby incorporated by reference for all that they disclose.
A typical optical scanner may include an optical imaging assembly comprising illumination, optical, and detection systems. The illumination source illuminates a portion of the object (commonly referred to as a "scan region"), whereas the optical system collects light reflected by the illuminated scan region and focuses a small area of the illuminated scan region (commonly referred to as a "scan line")onto the surface of a photosensitive detector positioned within the scanner. The photosensitive detector converts the image light incident thereon into electrical signals representative of the scan line. Image data representative of the entire object then may be obtained by sweeping the scan line across the entire object.
The term "image light" as used herein refers to the light reflected from the document and focused onto the surface of the detector array by the optical system. The image light may be converted into digital signals in essentially three steps. First, the photosensitive optical detector converts the light it receives into a varying electric current. Second, the varying electric currents from the detector elements are converted into analog voltages by an analog amplifier. Finally, the analog voltages are digitized by an analog-to-digital (A/D) converter. The digital data then may be processed and/or stored as desired.
While optical scanners of the type described above are being used, they are not without their problems. Image quality, scanner size and cost, and ease of assembly are related to the design and complexity of the optical imaging assembly. For example, the various components of the imaging assembly, i.e., the illumination source, the optical system and the detection system, must be precisely aligned to properly illuminate the document and focus the image light onto the detectors. The position, orientation, and distance of each element with respect to other elements must be correct to within close tolerances. Furthermore, the imaging assembly must be robust enough to resist shifting when the optical scanner is jolted or the operating environment varies.
If the illumination source is not properly aligned, the scan region may be too dark and the resulting image may lack contrast. If the image light is not properly focused and directed onto the detectors, the resulting image may be blurry or dark. Complex mounting and alignment systems may be employed to address these problems. However, a complex imaging assembly results in a relatively large, costly, and error prone optical scanner. Furthermore, the more complex the imaging assembly, the more difficult it is to assemble, and the more likely elements are to shift out of alignment.
Highly complex imaging assemblies also have a large tolerance stack. It is impossible to manufacture each part to the exact design measurements, therefore each part has a design tolerance, or an acceptable amount of error in size or shape. As parts are assembled together, the tolerance of each is added to a tolerance stack. Therefore, when elements of the imaging assembly are separated by a relatively large number of parts, the tolerance stack between the parts is relatively large, and the alignment error may be large enough to reduce image quality.
Consequently, a need exists for a smaller imaging assembly which is simple to assemble and align, resulting in a lower cost. A need further exists for an imaging assembly having a reduced tolerance stack to improve alignment and simplify assembly or repair.